6.5.2 Transcription: RNA Formation from the DNA Template

Question 1

Ribonucleic acid (RNA),

Answer 1

• as a nucleic acid polymer, consists of nucleotide subunits. RNA has ribose as its sugar whereas DNA has deoxyribose. RNA has the nitrogenous base uracil whereas DNA has thymine.
• Both DNA and RNA are polymers of nucleotide subunits. A nucleotide is made up of a phosphate group, a sugar, and a nitrogenous base. An RNA nucleotide differs from a DNA nucleotide in two main ways:
  1. RNA has a ribose sugar whereas DNA has a deoxyribose sugar. A ribose sugar has two hydroxyl groups; a deoxyribose sugar has one hydroxyl group.
  2. RNA has the nitrogenous base uracil whereas DNA has thymine.

Question 2

transcription

Answer 2

• During transcription, the growing messenger RNA strand is synthesized with the help of an enzyme, RNA polymerase, which links together the ribonucleotides. Both prokaryotic and eukaryotic DNA have a promoter, a specific nucleotide sequence that binds RNA polymerase and shows where RNA transcription will begin.
• begins when RNA polymerase recognizes
  the promoter, a sequence on the DNA strand located next to the segment that will be transcribed. The enzyme begins synthesizing the messenger RNA in a 5’ to 3’ direction. The mRNA strand is antiparallel to the DNA template meaning that their 5’ to 3’ orientations run in opposite directions.
• In eukaryotes, a TATA box is typically present in the
  promoter, consisting of a nucleotide sequences like
  “TATAAA”. The TATA box serves as a recognition site for
  proteins that aid RNA polymerase binding.
• In prokaryotes, the RNA polymerase specifically recognizes and binds directly to the promoter. In eukaryotes, a collection of proteins called transcription factors help RNA polymerase to recognize and bind to the promoter. The illustration shows the transcription initiation complex. The complex consists of RNA polymerase and protein transcription factors bound to the DNA double helix. The helix unwinds, and RNA synthesis begins at the startpoint of the template strand.

Question 3

What is the transcription unit?

Answer 3

• The sequence of DNA to be coded into mRNA

Question 4

_________________ a collection of proteins that help RNA polymerase recognize and bind to a promoter.

Answer 4

• Transcription factors are

Question 5

Which one of the following statements concerning a promoter is true?

Answer 5

• Once the promoter sequence is recognized, the new mRNA strand is synthesized in a 5′ to 3′ direction

Question 6

___________________ is a series of DNA nucleotides approximately 15 to 300 base pairs long, that serves as the site of RNA polymerase binding.

Answer 6

• The promoter region

Question 7

What aspect of transcription is the same for prokaryotes and eukaryotes?

Answer 7

• Transcription yields an mRNA strand, a complementary copy of a DNA strand.

Question 8

True or false?

RNA polymerase II reads in the same direction as DNA polymerase.

Answer 8

• true

Question 9

One of the three components of an RNA nucleotide is a ___________ sugar.

Answer 9

• ribose

Question 10

As RNA polymerase II moves along the DNA, it untwists one turn of the double helix at a time, exposing about _____________ bases for transcription.

Answer 10

• 10 to 20